Tom Ketchum was an ordinary man who was hunted by bounty hunters by accident. His resemblance to Black Jack Ketchum was uncanny and he couldn't prove he wasn't the wanted man.
The Judge had wanted posters distributed to the Dusters in order to bring Tom to him. However, the Banker, Rail Baron, and Rancher found himself first. They killed themselves, as their ancestors had before them, to hand the mantle over to Tom. Tom wasn't sure what to do besides find the real Black Jack Ketchum and sort things out.